Field
This invention is an invention regarding a mass flow controller and, not by way of limitation, this invention relates to a mass flow controller configured to control a mass flow rate based on a measured value of temperature or differential pressure of fluid.
Background
A mass flow rate control device (mass flow controller) is a control device constituted at least by a flow meter configured to measure a flow rate of a fluid, a flow control valve configured to control a flow rate of a fluid, a controlling circuit configured to control these and other parts. The mass flow controller has been widely used for the purpose of, for example, controlling a mass flow rate of a gas supplied into a chamber in a manufacturing process of a semiconductor, etc.
There are various types of flow meters used in mass flow controllers. In a mass flow controller used for the purpose of controlling a mass flow rate of a gas in a manufacturing process of a semiconductor, a thermal type flow meter or a pressure type flow meter has been mainly used. A flow rate of a gas measured by a flow meter is easily affected by influence of pressure of a gas to be measured. For example, in a case where pressure of a gas on an upstream side of a flow meter changes rapidly, etc., it becomes difficult to measure a flow rate correctly. For this reason, mass flow controllers comprising a mechanism for holding constant pressure of a gas on an upstream side of a flow meter for the purpose of measuring and controlling a flow rate correctly have been proposed.
For example, in the Patent Document 1 (Japanese Patent Application Laid-Open (kokai) No. 10-207554), an invention of a flow controller of a fluid characterized by detecting variation in pressure of the fluid on an inlet side where the fluid flows into and controlling, based on the detection result, such that the pressure of the fluid on an upstream side of a flow rate sensor (sensor unit) becomes constant is disclosed. In the Patent Document 1, an example of a configuration of a flow controller in which a pressure control mechanism (pressure control unit) is disposed on an upstream side of a flow rate sensor is described as an embodiment of the invention. This pressure controller monitors and detects change in pressure with a piezo-electric element and adjusts the pressure by varying a path of a pipe.
Moreover, for example, in the Patent Document 2 (Japanese Patent Application Laid-Open (kokai) No. 2003-280745), an invention of a mass flow controller which has a flow control valve and a flow sensor and is characterized by having a pressure control valve which is disposed on an upstream side of the flow control valve, a pressure sensor which is disposed between the pressure control valve and the flow control valve, and a control part which is configured to control the pressure control valve by feeding back an output of the pressure sensor is disclosed. In FIG. 1 of the Patent Document 2, a working example of a mass flow controller which uses a thermal type flow meter is disclosed as an embodiment of the invention.
In FIG. 4 of the Patent Document 2, an example of a semiconductor production line using a conventional mass flow controller is illustrated. In the semiconductor production line illustrated in this figure, a plurality of kinds of gases is supplied to a plurality of lines. In each gas supply line, a gas cylinder, a mechanical pressure regulator, a gauge, a filter and a mass flow controller are connected by a piping in this order from an upstream side toward a downstream side. The mechanical pressure regulator is prepared in order to supply a stable flow rate of a gas.
Furthermore, for example, in the Patent Document 3 (Japanese Patent Application Laid-Open (kokai) No. 2004-157719), an invention of a mass flow controller comprising a flow control valve, a flow rate detection means, a flow control valve disposed on an upstream side of the flow control valve, a pressure detection means disposed between the pressure control valve and the flow control valve, wherein the flow rate detection means is configured to detect differential pressure in a fluid which flows through the inside of a flow passage is disclosed. In FIG. 1 of the Patent Document 3, a configuration in which the thermal type mass flow meter of the mass flow controller disclosed in the Patent Document 2 is replaced with a pressure type mass flow meter is described as an embodiment of the invention.